Description:Ball- or cake-shaped, up to 20 cm high and 23 cm in diameter. Large specimens may show a shallow depression at their upper side, but many specimens are rounded or laterally expanded masses. Coarsely conulose; conules 2-15 mm high and 5-15 mm apart. One or more slight depressions with clusters of oscules; oscules 4-10 mm in diameter (I. strobulia-close up). Consistency tough.

Color:Blackish gray on the upper surface, yellow gray near the base.

Habitat:Common on reefs, but also on muddy sands and at bottoms at greater depths. Prefer brightly lit areas.